Manufacturing monocarboxylic acids



Patented Nov. 27, 1934 UNITED STATES.

MANUFACTURING MONOCARBOXYLIC ACIDS Johannes Brode, Ludwigshafen-on-the-Rhine, and Adolf Johannsen, Mannheim, Germany, assignors to I. G. Farbenindustrie Aktiengesellschait, Frankfort-on-the-Main, Germany, a corporation of Germany No Drawing. Original application November 19,

1926, Serial No. 149,520. Divided and this application April 21, 1928, Serial No. 271,970. In Germany November 27, 1925 8 Claims.

The present invention relates to the production of monocarboxylic acids from dicarboxylic acids or their anhydrides.

This application has been divided out from our copending application Ser. No. 149,520, filed November 19, 1926, now Patent No. 1,955,050, dated April 17, 1934 in which application we have described and claimed a process for the manufacture of monocarboxylic acids with the aid of catalysts capable of splitting off carbon dioxid. In the said process dicarboxylic acids or their anhydrides, the latter together with water vapor which, however, is preferably also added when starting from dicarboxylic acids, are passed, alone or together with other gases over the aforesaid catalysts at temperatures between about 250 and 500 C., preferably between 300 and 450 C. As stated in the aforesaid application Ser. No. 149,520, bismuth oxid is a particular Valuable catalyst whether employed alone or in conjunction with other compounds, such for example as oxids of other metals and the like.

The reaction is advantageously carried out with an excess of Water vapor over the quantity theoretically required; however, the process may also be carried out by exposing the vapor mixture formed by heating dicarboxylic acids (which mixture consists probably of the dicarboxylic acid, its anhydride and water vapor) directly over the catalyst. When starting from dicarboxylic acid anhydrides, an addition of water vapor to the anhydride vapor is necessary, as stated above.

The operation with a gas or air current containing water vapor offers often advantages over the use of water vapor alone, as, for example in the conversion of phthalic anhydride into benzoic acid, the concentration of the water vapor and the temperature at which the separation of j the reaction products takes place, may be so chosen as to obtain the reaction product directly in a solid, practically dry form; this results in the purification and further use of the reaction product being much facilitated.

The dicarboxylic acid anhydrides employed as initial materials in the process above mentioned, for example phthalic anhydride, maleic anhydride and the like, may be obtained by the catalytic oxidation of vapors of hydrocarbons or their derivatives such as naphthalene, naphthol, benzene, phenol and the like.

We have further found that when the dicarboxylic acid anhydrides are prepared by catalytic reactions in the vapor phase, such for example as have been mentioned before, it is not necessary to separate the anhydride from the reaction mixture, but the latter may be passed directly or after an addition of water vapor has been made, over the catalyst capable of splitting oif carbon dioxid. This method or working is of particular advantage when the anhydrides are prepared by the catalytic oxidation of hydrocarbons or derivatives thereof.

The following example will further illustrate how our invention may be carried out in practice, but the invention is not limited to this example.

Example Nitrogen saturated at about 30 C. with water vapor is passed over phthalic acid maintained at a temperature of about 180 to 200 C. The mixture of gases and vapors thus formed is passed over a mixture of bismuth oxid and aluminum oxid precipitated on pumice stone, and maintained at a temperature of about 340 to 360 C. The gas mixture leaving the reaction vessel is cooled whereby dry very pure benzoic acid is separated in a good yield.

What we claim is:

1. The process of producing monocarboxylic acids which comprises passing the vapors of a dicarboxylic acid at between about 250 and about 500 C. over a catalyst essentially comprising bismuth oxid.

2. The process of producing monocarboxylic acids which comprises passing the vapors of a dicarboxylic acid together with water vapor at between about 250 and about 500 C. over a catalyst essentially comprising bismuth oxid.

3. The process of producing monocarboxylic acids which comprises passing the vapors of a dicarboxylic acid anhydride together with water vapor at between about 250 and about 500 C. over a catalyst essentially comprising bismuth oxid.

4. The process of producing monocarboxylic acids which comprises passing the vapors of a dicarboxylic acid anhydride together with water vapor at between about 300 and about 450 C. over a catalyst essentially comprising bismuth oxid.

5. The process of producing benzoic acid which comprises passing phthalic anhydride vapor together with water vapor at between about 250 and about 500 C. over a catalyst essentially comprising bismuth oxid.

6. The process of producing benzoic acid which comprises passing phthalic anhydride vapor together with water vapor over a mixture essentially comprising bismuth oxid and aluminium oxid 8. The process of producing'benzoic acid which comprises subjecting naphthalene vapor to a catalytic oxidation to phthalic anhydride and passing the resulting gas mixture at between about 250 and about 500 C. over a catalyst essentially comprising bismuth oxid.

J OHANNES BRODE. ADOLF J OHANNSEN. 

